1. Field of the Invention
The present invention relates to a medical imaging system including an X-ray imaging apparatus provided with a Talbot interferometer or Talbot-Lau interferometer.
2. Description of Related Art
It is quite difficult to capture X-ray absorption images (i.e., common X-ray images captured with traditional silver halide films) of patient's joint cartilage.
Magnetic resonance imaging (MRI), which can image joint cartilage, requires a high-cost apparatus and has high running costs and thus has increased inspection costs. Besides, MRI produces low resolution images that involve, for example, a risk of inaccurate measurement of the thickness of cartilage.
With MRI, a doctor specialized in imaging diagnostic estimates the thickness or other features of cartilage from captured images, on the basis of knowledge or experience, in many cases. A doctor, who is not specialized in imaging diagnostic, cannot determine the features from such low resolution images and has no choice but to relay on the specialist's estimation.
A conventional diagnosis of rheumatoid arthritis or osteoarthritis includes capturing an X-ray image (i.e., absorption image) of a joint such as a finger or knee joint. The doctor estimates the thickness, abrasion, or other states of the cartilage that is not visualized in the image, from the distance of a gap in the joint (i.e., the distance of a gap between two bones forming the joint) shown in the X-ray image.
The inventor of the present invention et al. have studied an X-ray imaging apparatus provided with a Talbot interferometer using the Talbot effect, which achieves imaging by sensing phase shifts in X-rays passing through an object, and an X-ray imaging apparatus provided with a Talbot-Lau interferometer which is an application of the Talbot interferometer (see Japanese Unexamined Patent Application Publication No. 2008-200359 and WO 2011/033798, for example). These interferometers are known to achieve imaging of mammary tissue and any other tissue which are not likely to appear on usual X-ray absorption images due to a small X-ray absorptive difference.
As described later, an X-ray imaging apparatus provided with a Talbot interferometer or Talbot-Lau interferometer is known to produce moire images which can be reconstructed into at least three types of images by a scheme using the principle of fringe scanning (see K. Hibino et al, J. Opt. Soc. Am. A, Vol. 12, (1995), pp. 761-768; and A. Momose et al, J. Appl. Phys., Vol. 45, (2006), pp. 5254-5262, for example) or by the Fourier transform (see M. Takeda et al, J. Opt. Soc. Am, Vol. 72, No. 1, (1982), p. 156, for example).
The three types of images consist of an absorption image (i.e., usual X-ray absorption image) reflecting the contrast produced by X-ray absorption, a differential phase image reflecting the contrast based on phase information, and a small-angle scattering image reflecting the contrast produced by small-angle scattering.
The inventor of the present invention et al. have applied such X-ray technology using a Talbot interferometer or Talbot-Lau interferometer to imaging of joint cartilage and found that an X-ray imaging apparatus provided with a Talbot interferometer or Talbot-Lau interferometer can produce at least differential phase images of cartilage in a cadaveric joint, as disclosed in Nagashima, Masabumi and seven others. “Optimization of Joint and Cartilage: Diagnostic Potential of Differential Interferential Contrast X-ray Imaging”. Proceedings of the 14th Japanese Research Society of Clinical Anatomy, 2010-09-11. Japanese Research Society of Clinical Anatomy, February 2011, No. 11, pp. 56-57, http://www.jrsca.jp/contents/records/contents/PDF/11-PDF/p5 6.pdf (accessed on Dec. 11, 2012).
As described later, an improved X-ray imaging apparatus provided with a Talbot interferometer or Talbot-Lau interferometer successfully captures a moire image of a joint in a living body instead of a cadaveric joint and reconstructs the image to produce at least a differential phase image of joint cartilage.
This technology allows the thickness or other features of cartilage to be accurately measured from a reconstructed image, and thus provides a medical imaging system which allows quantitative measurement of the thickness or other features of cartilage.